Actually, on my Android phone I'm constantly using a third party task killer to stop services and apps running in the background that I thought I 'quit' by backing out of them. I also use the quit option on apps that have it.

I don't entirely trust Android to manage battery life as efficiently as possible yet, especially when iPhone still does it so much better, and when every time I check the services running on the phone, there seem to be tons I had never even started in the first place.

I consider that at least partly a UI/UX issue.

(On a side note, that's my only complaint about Android so far, using 2.3, otherwise it's great.)